Implantable medical devices, particularly pacemakers, are often configured to be used in conjunction with an external programmer which allows a physician to control the implantable medical device and to display information sensed by the device. For example, with a pacemaker, the external programmer may operate to control the parameters by which the pacemaker paces the heart and to display intracardiac electrograms (IEGMs) and other useful diagnostic information.
One example of an external programmer for use with a pacemaker is an analyzer-programmer system (APS) identified as the APS II system which is provided by St. Jude Medical CRMD of Sylmar, Calif. Components of the APS II system operate to allow a physician to program the operation of the pacemaker to, for example, control the manner by which the pacemaker detects arrhythmia conditions within the heart and responds thereto. In particular, the APS II system allows the physician to specify atrial and ventricular sensitivity threshold values with which the pacemaker senses P-waves and R-waves within, respectively, the atrium and ventricle of the heart and to further specify the mode employed by the pacemaker for pacing the heart in circumstances where expected P-waves or R-waves are not-sensed. An exemplary single-chambered pacing mode is VVI wherein both pacing and sensing is performed in the ventricle and wherein, upon detection of an R-wave, subsequent pacing within the ventricle is inhibited for a predetermined pacing interval. An exemplary dual-chambered pacing mode is VDD wherein sensing is performed in both the atrium and the ventricle but pacing is performed only in the ventricle. With the VDD mode, which is also referred to as the P tracking mode, detection of an R-wave in the ventricle triggers a pacing pulse, then further pacing is inhibited for the duration of the pacing interval. U.S. Pat. No. 5,487,755, to Snell et al. entitled "Method for Displaying a Sequential Series of Pacing Events" provides a detailed description of the operation of the APS II system of St. Jude Medical CRMD (formerly Pacesetter, Inc.) including a description of various pacing modes. U.S. Pat. No. 5,487,755 is incorporated by reference herein.
It is particularly important that the atrial and ventricular sensitivity threshold values are set optimally to ensure that P-waves and R-waves are properly detected so that the correct pacing action is taken by the pacemaker based upon the selected pacing mode. If the sensitivity threshold values are set too low, then random noise spikes may be misinterpreted as P-waves or R-waves and incorrect action may be taken by the pacemaker, perhaps resulting in the failure to provide pacing pulses when otherwise required. If the sensitivity threshold values are set too high, then P-waves or R-waves that are actually present may go undetected and again incorrect action maybe taken by the pacemaker including, for example, providing a pacing pulse when none is needed, perhaps triggering pacemaker mediated tachycardia (PMT). Although the atrial and ventricular sensitivity threshold values are typically not the only factors employed to determine whether a sensed electrical signal is a P-wave or an R-wave, the sensitivity threshold values are key factors in that determination and optimal sensitivity threshold values are critical for the safe and reliable operation of the pacemaker.
Although the aforementioned APS II system provides much useful diagnostic information to assist a physician in setting or adjusting the atrial and ventricular sensitivity values, room for further improvement remains. In particular, it would be desirable to provide a diagnostic display which allows the physician to easily visually verify that the atrial and ventricular sensitivity threshold values are properly set and it is primarily to that end that the present invention is directed. Additionally, it would be desirable to provide a method whereby the sensitivity threshold values may be automatically adjusted to a more optimal value by the pacemaker itself and aspects of the present invention are directed to that end as well.